Aug. 21, 2008 -- Plastics made from renewable resources such as corn are attractive because they are biodegradable, but recent studies suggest they have the added benefit of generating lower greenhouse gas emissions than conventional petroleum-based plastics.
Jian Yu and Lilian Chen of the University of Hawaii, Honolulu, examined the greenhouse gas emissions associated with producing one type of bioplastic, polyhydroxyalkanoates (PHA), made by bacteria growing on corn-based sugar.
The pair examined the potential for making PHA from waste material left over from the production of ethanol from the stalks and leaves of corn plants -- which is not yet done on a commercial scale.
"We count all of the chemicals, fertilizers and fuels. We also count the CO2 released from our process. That includes the direct CO2 from the fermentation part, and the energy part," Yu said. "We tried to bean count so we can understand which part is the major CO2 producer."
The researchers found that PHA production generated the equivalent of 0.49 pounds of carbon dioxide for every pound of plastic, compared to two to three pounds of carbon dioxide for every pound of conventional plastic. They published their results in Environmental Science and Technology.
Other bioplastics look even better. Polylactide (PLA), produced commercially by Minnesota-based NatureWorks, LLC, generates 0.27 pounds of carbon dioxide for every pound of plastic produced, according to results published last year in Industrial Biotechnology.
This represents an 85 percent reduction compared with the company's 2003 analysis of the process, which was then operating at a smaller scale.
"We looked at all of the places we were emitting greenhouse gases," NatureWorks' Erwin Vink told Discovery News. "We found that the biggest contributor is the fermentation process, and the other big contributor is electricity. So, we developed a new process technology, not only for environmental reasons, but for economic reasons. That gave significant reductions in greenhouse gases."
The company also purchased renewable energy certificates to offset their electricity use.
The major reason bioplastics have a favorable carbon footprint is that they are made from renewable plant sources of carbon, instead of from oil, both Vink and Yu said.
Since both processes are relatively new, there should be room to further improve the footprints of both, compared with conventional plastic manufacturing, which has been optimized over years of production.
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